power electronics

POWER ELECTRONICSPOWER ELECTRONICS

INTRODUCTION TO INTRODUCTION TO POWER ELECTRONICSPOWER ELECTRONICS

Dr. Adel GastliEmail: [email protected]

http://adel.gastli.net

Dr. Adel Gastli Power Electronics: Introduction 2

CONTENTSCONTENTSCONTENTS1. Definitions and History2. Applications of Power Electronics3. Power Semiconductor Devices4. Control characteristics of power devices5. Characteristics & specifications of switches6. Design of power electronics equipment7. Rms values of waveforms8. Types of power electronic circuits9. Peripheral effects10. Power modules11. Intelligent modules12. Journals & References


DEFINITION & HISTORYDEFINITION & HISTORY

Power electronics refers to control and conversion of electrical power by power semiconductor devices wherein these devices operate as switches.

Advent of Silicon-Controlled Rectifiers, abbreviated as SCRs, led to the development of a new area of application called the Power Electronics.


Prior to the introduction of SCRs, mercury-arc rectifiers (1900) were used for controlling electrical power, but such rectifier circuits were part of industrial electronics and the scope for applications of mercury-arc rectifiers was limited.

Once the SCRs were available (1957), the application area spread to many fields such as drives, power supplies, aviation electronics, high frequency inverters and power electronics originated.


APPLICATIONS OF POWER APPLICATIONS OF POWER ELECTRONICSELECTRONICS

Power electronics has applications that span the whole field of electrical power systems, with the power range of these applications extending from a few VA/Watts to several MVA/MW.

The main task of power electronics is to control and convert electrical power from one form to another form.


Power electronics is a subject of interdisciplinary nature.

Electronics Devices|Circuits

Power Equipment

Static|Rotating

ControlAnalog|Digital

Power

Electronics


Some Applications of Power Electronics

AdvertingAir conditioningAircraft power suppliesAlarmsHousehold AppliancesBattery chargerChemical processingComputersCranes, hoists, elevatorsDimmersDisplaysElectric door openersElectric dryers, fans

Electric vehicles & tractionElectromagnetsGas turbine startingGenerator excitersHigh voltage dc (HVDC)Motor drivesMovie projectorOil well drillingPaper millsPhotograph, photocopy machinesTV, Radio, VCRSolar power supplies, etc…


POWER SEMICONDUCTOR DEVICES

Since the first thyristor (SCR) was developed in late 1957, there has been tremendous advances in the power semiconductor devices.

Since 1970 various types of power semiconductor devices were developed and became commercially available.



Power semiconductor devices are made of either silicon or silicon carbide.

These devices can be divided broadly into three main types:

Power diodes

Thyristors

Transistors


Classification of power semiconductors


Power DiodesPower Diodes

General purposeRating up to 6000V, 4500A

High speed (or fast recovery)Rating up to 6000V, 1100A

Reverse recovery time 0.1 to 5μs

Essential for high-frequency switching


Power Diodes (cont.)

SchottkyLow on-state voltage

Very small recover time (typically nanoseconds).

Leakage current increases with voltage rating

Rating limited to 100V, 300A


Power Diodes (cont.)

Conducts when its anode voltage is higher then that of the cathode (VA > VC)

Forward voltage drop (when on) is very low (typically 0.5 and 1.2V)

If VC > VA the diode is said to be in blocking mode.

Anode Cathode

2 terminals


Stud-mounted type

Disk, press pak, or hokey puck type


ThyristorsThyristors

When a small current is passed through the gate terminal to cathode, the thyristor conducts provided that the anode terminal is at higher potential than that of the cathode:

iG >0VA > VC

3 terminals

Anode CathodeGate


Thyristors (Cont.)

Once a Thyristor is in a conduction mode, the gate circuit has no control and the thyristor continues to conduct.In conduction mode, forward voltage is very small (0.5 to 2 V).Thyristor can be turned off by making VAC ≤ 0V

Line-commutated thyristors are turned off due to the sinusoidal nature of their input voltageForced-commutated thyristors are turned off by an extra circuit called commutation circuitry.


Thyristors (Cont.)

Natural or line-commutated thyristors are available with rating up to 6000 V, 4500A.

Turn-off-time became very small (10 to 20 μs in 3000 V, 3600A).

Instant when the principle current has decreased to zero after external switching of the principle voltage circuit

Instant when thyristor is capable of supporting a specified voltage without turning on.

ti=0 tVAC≠0Turn-off-time


Thyristors (Cont.)

Can be subdivided into 11 types:1. Forced-commutated

2. Line-commutated

3. Gate-Turn-Off (GTO)

4. Reverse Conducting Thyristor (RCT)

5. Static Induction Thyristor (SITH)

6. Gate-Assisted turn off Thyristor (GATT)

7. Light-activated Silicon-Controlled Rectifier (LASCR)

8. MOS Turn-Off (MTO)

9. Emitter Turn-Off (ETO)

10. Integrated Gate-Commutated Thyristor (IGCT)

11.MOS Controlled Thyristors (MCTs)


SelfSelf--Study Study (Outcome i: a(Outcome i: a recognition of the need for, and recognition of the need for, and

an ability to engage in lifean ability to engage in life--long learning)long learning)

Page 8: main characteristics and applications of different types of thyristors.


Power TransistorsPower TransistorsThere are 4 types:

Bipolar Junction Transistors (BJTs)

Power MOSFETS

Insulated-Gate Bipolar Transistors (IGBTs)

Static Induction Transistors (SITs)


Power Transistors (Cont.)Power Transistors (Cont.)Bipolar Junction Transistors (BJTs)

Used in power converters at frequency below 10 kHz

Power ratings up to 1200V, 400A.

VBE> 0, IB >ITH conduction (on) mode

VBE< 0, IB <ITH nonconduction (off) mode

C

E

B

IE

ICIB

IB1

IBn IBn> IB1

IB2

VCE

IC

0saturation

Operates like a switch (on-off)

NPN-BJT


Power Transistors (Cont.)Power Transistors (Cont.)Power MOSFETs

Used in high-speed power converters at frequency range of several tens of kHz.

Power ratings up to 1000V, 100A (relatively low power ratings).

D

S

G

ID

VGSn

VGS1> VGSn

VDS

ID

0

N-channel VGS0


Power Transistors (Cont.)Power Transistors (Cont.)IGBTs

Voltage controlled power transistors (better drive circuit) faster than BJTs but slower than MOSFETs.

Used in power converters at frequency up to 20 kHz

Power ratings up to 1700V, 2400A (high voltage high current).

C

E

G

IE

ICVGE1

VGEn VGEn> VGE1

VCE

IC

0

VT


Power Transistors (Cont.)Power Transistors (Cont.)SITs

Used in high-power high frequency applications (audio, VHF/UHF, and microwave amplifiers)

Power ratings up to 1200V, 300A.

Has low-noise, low-distortion, high-audio-frequency power capability.

Very short turn-on and turn-off times (typically 0.25μs)

On-characteristic and high on-state drop limit its applications for general power conversions.

D

S

G

IS

ID

VGSn

VGSn> VGS1

VDS

ID

0

VGS1=0V


Power ranges of commercially available power semiconductor devices

100 200 500 1000 2400 4000 6000 10000 I [A]

100

200

1000

550060007500

12000

1000 V/100A(SanRex)

60 V/1000A(Semikron)

IGCT (Market)

SCR (Market)

IGBT (Market) GTO (Market)

6500V/600A(Eupec)

12000V/1500A(Mitsubishi)

7500V/1650A(Eupec) 6500V/2650A

(ABB)

5500V/2300A(ABB)

6000V/6000A GTO(Mitsubishi)

6000V/6000A IGCT(Mitsubishi announced)

4800V/5000A(Westcode)

4500V/4000A(Mitsubishi)

V [V]

Power MOSFET (Market)



CONTROL CHARACTERISTICS OF POWER DEVICES

+Input

voltage Vs

_

Gate signal vG

R

+Output voltage

v0_

Thyristorv0

Vs

vG

0

-1

1Thyristor switch

First pulse turns it on and stays always on


+Input

voltage Vs

_

+vG

_

R

+Output voltage

v0_

GTO

v0Vs

vG

0

-1

1

GTO/MTO/ETO/IGCT/MCT/SITH switch

Positive pulse turns them on and negative pulse turns them off

KA

KA

SITH

KAG

MCT

t1 T t

Polarity of vG

is reversed for MCT


+Input

voltage Vs

_

R

+Output voltage

v0_

v0Vs

vB/vGS

0

1

BJT/MOSFET/IGBT switch

Positive voltage turns them on and zero voltage turns them off

vB +

t1 T t

t1 T t

+Input

voltage Vs

_

R

+Output voltage

v0_

vGS +

C E

G

D S


Classification1. Uncontrolled turn on and turn off (e.g. diode)

2. Controlled turn on and uncontrolled turn off (e.g. SCR)

3. Controlled turn on and off (e.g. BJT, MOSFET, IGBT, GTO, SITH, SIT, MCT)

4. Continuous gate signal requirement (e.g. BJT, MOSFET, IGBT, SIT)

5. Pulse gate requirement (e.g. SCR, GTO,MCT)

6. Bipolar voltage-withstanding capability (e.g. SCR, GTO)

7. Unipolar voltage-withstanding capability (e.g. BJT, MOSFET,GTO, IGBT, MCT)

8. Bidirectional current capability (e.g. TRIAC, RCT)

9. Unidirectional current capability (e.g. SCR, GTO, BJT, MOSFET, MCT,IGBT, SITH, SIT, Diode)

(See Table 1.4 page 15 of the textbook)


CHARACTERISTICS & SPECIFICATIONS OF SWITCHES

On state: carry high forward current, IF= ∞Low forward voltage drop, VON=0low on-state resistance, RON=0

Off state:High forward or reverse voltage, VBR =∞Low off-state leak current, IOFF=0High off-state resistance, ROFF=∞(low off-state power losses)

Requires very low thermal impedance from internal junction to ambient, RJA=0, so that it transmits heat easily to the ambient Must have high i2t, to sustain any fault current for a long time.

Turn-on & turn-off processes:Controllable

• Must turn on with gate signal (e.g. positive)

• Must turn off with another gate signal (e.g. zero or negative)

Instantaneous (high frequency)• Low delay time, td=0• Low rise time, tr=0• Low storage time, ts=0• Low fall time, tf=0

Low gate-drive power, PG=0Low gate-drive voltage, VG=0Low gate-drive current, IG=0

Device must be capable of handling rapid voltage changes across it, dv/dt= ∞Device must be capable of handling rapid current changes across it, di/dt= ∞

Ideal SwitchIdeal Switch


Practical DevicesPractical Devices VCC

vSW

iSW

iG

vG

PSW

VSW(sat)

ISWs

ISW0

IG(sat)

VG(sat)

Ts=1/fs

ton toff

td tr tn ts tf t0

t

t

t

t

t

+VSW

_+_

VG

IG

iSW

RL

VCC

Controlled switch

Switching power losses

GSWOND

ttt

sSW

t

sON

PPPP

pdtpdtpdtfP

pdtT

P

fsr

ON

++=

⎟⎠⎞⎜

⎝⎛ ++=

=

∫∫∫

∫

000

0

1

Conduction Switching Gate-driver power losses power losses power


Switch SpecificationsSwitch SpecificationsVoltage ratings

Forward & reverse repetitive peak voltagesOn-state forward drop-voltage drop

Current ratingsAverage, rms, repetitive peak, nonrepetitive peak, off-state leakage

Switching speed or frequency

di/dtdv/dtSwitching lossesGate drive requirementsSafe operating area (SOA): limits on the allowable steady-state operating points in the v-icoordinatesI2t for fusingTemperaturesThermal resistance


Device ChoicesDevice Choices

Non of the existing switching devices is ideal.

For high power applications from the ac 50-60Hz main supply, phase control and bidirectional thyristors are the most economical choices.

COOLMOS and IGBTs are potential replacements for MOSFETS and BJTs, respectively, in low and medium power applications.


Device Choices (cont.)Device Choices (cont.)

GTOs and IGCTs are most suited for high-power applications requiring forced commutation.

With the increased advances in technology, IGBTs are increasingly employed in high-power applications and MCTs may find potential applications that require bidirectional blocking voltages.


DESIGN OF POWER ELECTRONICS EQUIPMENT

1. Design of power circuits

2. Protection of power devices

3. Determination of control strategy

4. Design of logic and gating circuits


In this course, power devices are assumed ideal switches unless stated otherwise.Effect of stray inductance, circuit resistances, and source inductance are usually neglected.Before prototype is built, the designer should investigate the effects of the circuit parameters and device imperfections. The design should be modified if necessary.Only after the prototype is built and tested, the designer can be confident about the validity of the design proposed and can estimate more accurately some circuit parameters (e.g. stray inductance).


RMS VALUES OF WAVEFORMS

rms values of current waveforms must be known:

To accurately determine losses in a device

To accurately determine current ratings of the device and components

Current waveforms are rarely sinusoids or rectangles


∫=T

rms dtiT

I0

21

Time period

If a waveform can be broken into harmonics whose rms values can be calculated individually, the rms value of the actual waveform can be approximated satisfactory as:

2)(

2)2(

2)1(

2nrmsrmsrmsdcrms IIIII +++= L

Harmonics rms valuesdc component

See page 25 (Fig. 1.17) for some rms values of commonly encountered waveforms


Problems Solving:Problems Solving:

Find the average and rms values of the following waveforms.

vo100V

t8ms 20ms

0 π 2π

vo100V

ωt

0 π 2π

vo100V

ωt

0 π/2 π 2π

vo100V

ωt


TYPES OF POWER ELECTRONIC CIRCUITS

Diode rectifiers

Ac-dc converters (controlled rectifiers)

Ac-ac converters (ac voltage controllers)

Dc-dc converters (dc choppers)

Dc-ac converters (inverters)

Static switches (ac or dc)


Diode rectifiersConverts ac into a fixed dc voltage.

Input could be either single phase or three phase

tVv ms ωsin=

0 π 2π

Vm

vs

ωt

0 π 2π

voVm

ωt

Diode D1

+

_

Diode D2

+

_viac supply

Load resistance R

vs

vo+ –

tVv ms ωsin=

Find the expressions of average and rms values.


Ac-dc convertersConverts ac into a variable dc voltage.


vo

Thyristor T1

+

_

Thyristor T2

+

_viac supply

Load resistance R

vs

vo+ –

tVv ms ωsin=

tVv ms ωsin=

0 π 2π

Vm

vs

ωt

-Vm

α

0 π 2π

Vm

ωtα

Find the expressions of average and rms values as a function of α.


Ac-ac convertersConverts fixed ac into a variable ac voltage.


tVv ms ωsin=

0 π 2π

Vm

vs

ωt

-Vmac supply

Triac

Load resistance R

+

–

votVv ms ωsin=

0 π 2π

voVm

ωtα

α

Find the expressions of average and rms values as a function of α.


Dc-dc converters (Choppers)

Converts fixed dc into a variable dc voltage.

dc supply

0 t1 Τ

vo

1vs

Vs

ωt

ωt

Load

+

–

vo

+

vs

–

TransistorQ1

+ _VGE

V0=δVs

T

t1=δ Duty cycle


Dc-ac converters (Inverters)

Converts fixed dc into a variable ac voltage.

Output can be single phase or three phase

dc supply

0 T/2 T

vo

1vg1, vg2

vs

ωt

ωt

Load

+

vo

+

vs

–

+vg1 vg3

M1 M3

M4 M2

+ __ _

G

G G

G ωtvg3, vg4

-vs


Static switches

Power electronic devices can operate as static switches or contactors to transmit either ac or dc power to loads.

Mains 2

Rectifier/charger Inverter Isolation transformer

Static bypassswitch

Mains 1Load

Battery

Example: Uninterruptible Power Supply (UPS)

ac supply


PERIPHERIAL EFFECTS(Effects of Power Converters)

ProblemsProblems: Introduce current and voltage harmonics into the supply system and on converters output.

Distortion of the output voltage.

Harmonic generation into supply system

Interference with communication and signaling circuits


SolutionsSolutions: It is normally necessary to introduce filters in the input and output of a converter system to reduce the harmonic level to an acceptable magnitude.

Input filter

Output filter

Power converter

Switching control signal

generator

PowerSource

Output


Power quality issuesPower quality issues

Application of power electronics poses a challenge on the power quality issues and raises problems and concerns to be resolved by researchers.Important factors that measure the quality of a waveform are:

Total harmonic distortion (THD)Displacement Factor (DF)Input power factor (IPF)

Harmonic content of the waveforms is required to find these factors.


To evaluate the performance of a converter, the input and output voltages and currents of a converter are expressed in a Fourier seriesFourier series.

The control strategycontrol strategy of a power converter play an important part on the harmonic generation and output waveform distortion, and can be aimed to minimize or reduce these problems.

Electromagnetic radiation and interference can be avoided by grounded shielding.


POWER MODULES

Power devices are available as a single unit or a module.

A power converter often requires two, four, or six devices, depending on its topology.

Power modules with dual (in half-bridge configuration), or quad (in full bridge) or six (in three phase) are available for almost all types of power devices.


Modules offer the advantages of

lower on-state losses,

high voltage and current switching characteristics,

high speed (switching frequency)

Some modules include transient protection and gate drive circuitry.

Gate drive circuits are commercially available to drive individual devices or modules.


INTELLIGENT MODULES

Intelligent modules, which are the state of the art of power electronics, integrate the power module and the peripheral circuit.Peripheral circuits consists of:

Input or output isolation from, and interface with, the signal and high-voltage system, A drive circuitProtection and diagnostic circuitMicrocomputer controlControl power supply


Users need only to connect external (floating) power supplies.

An intelligent module is also known as smart power.

Smart power technology can be viewed as a box that interfaces power source to any load.

These modules are used increasingly in power electronics.

: list of websites of some manufacturers of these modules


JOURNAL & REFERENCES

See section 1.11 in your textbook at page 28.

Search the internet for more recent sites (keywords: power electronics, tutorials, circuits, devices,…)

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converts fixed

variable ac

bipolar junction

variable dc

power semiconductor

load resistance

power transistors